Blacktip Shark
The Blacktip Shark is a species of requiem shark, family Carcharhinidae. Normally wary of humans, blacktip sharks can become aggressive in the presence of food and have been responsible for a number of attacks on people. This species is of importance to both commercial and recreational fisheries across many parts of its range, with its meat, skin, fins, and liver oil used. It has been assessed as Near Threatened by the International Union for Conservation of Nature (IUCN), on the basis of its low reproductive rate and high value to fishers. Description The blacktip shark has a robust, streamlined body with a long, pointed snout and relatively small eyes. The five pairs of gill slits are longer than those of similar requiem shark species. The jaws contain 15 tooth rows on either side, with 2 symphysial teeth (at the jaw midline) in the upper jaw and 1 symphysial tooth in the lower jaw. The teeth are broad-based with a high, narrow cusp and serrated edges. The first dorsal fin is tall and falcate (sickle-shaped) with a short free rear tip; there is no ridge running between the first and second dorsal fins. The large pectoral fins are falcate and pointed. The coloration is gray to brown above and white below, with a conspicuous white stripe running along the sides. The pectoral fins, second dorsal fin, and the lower lobe of the caudal fin usually have black tips. The pelvic fins and rarely the anal fin may also be black-tipped. The first dorsal fin and the upper lobe of the caudal fin typically have black edges. Some larger individuals have unmarked or nearly unmarked fins. Blacktip sharks can temporarily lose almost all their colors during blooms, or "whitings", of coccolithophores. This species attains a maximum known length of 2.8 m (9.0 ft), though 1.5 m (4.9 ft) is more typical, and a maximum known weight of 123 kg (271 lb). Habitat Most blacktip sharks are found in water less than 30 m (100 ft) deep over continental and insular shelves, though they may dive to 64 m (210 ft). Favored habitats are muddy bays, island lagoons, and the drop-offs near coral reefs; they are also tolerant of low salinity and enter estuaries and mangrove swamps. Although an individual may be found some distance offshore, blacktip sharks do not inhabit oceanic waters. Food Fish make up some 90% of the blacktip shark's diet. A wide variety of fish have been recorded as prey for this species: sardines, herring, anchovies, ladyfish, seacatfish, cornetfish, flatfish, threadfins, mullet, mackerel, jacks, groupers, snook, porgies, mojarras,emperors, grunts, butterfish, tilapia, triggerfish, boxfish, and porcupinefish. They also feed on rays and skates, as well as smaller sharks such as smoothhounds and sharpnose sharks. Crustaceans and cephalopods are occasionally taken. In the Gulf of Mexico, the most important prey of the blacktip shark is the Gulf menhaden (Brevoortia patronus), followed by the Atlantic croaker (Micropogonias undulatus). Off South Africa, jacks and herring are the most important prey. Behavior Like the spinner shark, the blacktip shark is known to leap out of the water and spin three to four times about its axis before landing. Some of these jumps are the end product of feeding runs, in which the shark corkscrews vertically through schools of small fish and its momentum launches it into the air. Observations in the Bahamas suggest that blacktip sharks may also jump out of the water to dislodge attached sharksuckers (Echeneis naucrates), which irritate the shark's skin and compromise its hydrodynamic shape. The speed attained by the shark during these jumps has been estimated to average 6.3 m/s (21 ft/s). Blacktip sharks have a timid disposition and consistently lose out to Galapagos sharks (C. galapagensis) and silvertip sharks (C. albimarginatus) of equal size when competing for food. If threatened or challenged, they may perform an agonistic display: the shark swims towards the threat and then turns away, while rolling from side to side, lowering its pectoral fins, tilting its head and tail upwards, and making sideways biting motions. The entire sequence lasts around 25 seconds. This behavior is similar to the actions of a shark attempting to move a sharksucker; it is possible that one of these behaviors is derived from the other. Category:Fish Category:Meat Eater Category:Cold Blooded Category:Viviparous